The influences were investigated of various operating parameters on beat transmission, i.e. the evaporative capacity, in a single vertical evaporator tube, fed with pure water.

With natural circulation, temperature level and difference had a pronounced influence, especially at lower values of these parameters (e.g. boiling temperature 40°C, temperature difference 15°C). The heat transmission coefficient k increased for increasing temperature level as well as for increasing temperature difference.

The influence of the apparent liquid level was very important and was more pronounced for lower temperature levels and smaller differences. For each set of operating temperatures an apparent liquid level existed, for which k was maximum. The apparent liquid level had a very big influence on circulation rate. Forced circulation induced higher values of k only if the forced circulation rate was much higher than the natural one. Because natural circulation was slow for low temperatures and small differences forced circulation was found to be advantageous in these conditions.

With forced circulation the influence of temperature difference on k was small and sometimes reversed. Due to decreased viscosity, k was higher at higher temperatures. The most important influence on k was exerted by forced circulation rate.

With flash evaporation k was generally slightly smaller than with forced circulation, except at high circulation rates, where k became equal for both systems.